Telecommunication cables

ABSTRACT

A telecommunication cable comprises at least two cable units laid up together and enclosed in a water-proof sheath. Each cable unit comprises a multiplicity of conductors each having a dielectric of cellular plastics material, at least one layer of insulating tape, for instance paper, surrounding the multiplicity of conductors and, filling the interstices within the cable unit, a water-impermeable medium, for instance petroleum jelly, which will not drain under the influence of gravity or such hydrostatic pressure as may arise in the event of damage to the cable sheath but which will permit relative sliding movement of the cellular plastics insulated conductors over one another during such bending of the cable as occurs during manufacture and installation of the cable. The or each layer of insulating tape is impregnated with the water-impermeable medium and constitute a barrier to the ingress of water.

United States Patent Boult I [54] TELECOMMUNICATION CABLES [72] Inventor: David Luard Bouit, Manley, En-

gland [73] Assignee: British Insulated Callenders Cables Limited, London, England [22] Filed; Nov. 20, 1970 [21] Appl. No.: 91,507

[30 Foreign Application Priority Data Nov. 19, 1969 Great Britain ..56,711/69 [52] US. Cl ..l74/25 R, l56/48Q156/52, 174/113 R,-'174'/116 [51] Int. Cl. ..H0lb 7/02 581 Field or soaroh... 1 4( 116, 103, 107,113, 124 R, 174/120 R, 25 c, 25 R, 23 R,26, 114 s, 114

R, 117 FF, 119 R, 119 C; 29/624; 156/48,

[56] References Cited UNITED STATES PATENTS 1,904,162 4/1933 Milliken ..174/114 S 2,269,877 1/1942 Johnson.... 3,420,720 1/1969 Hillman.... 3,244,799 4/1966 Roberts 3,271,508 9/1966 Burr 3,525,798 8/1970 A .4?? we w 7 14 1 Dec.19,1972

FOREIGN PATENTS OR APPLICATIONS 995,582 6/1965 Great Britain ..l74/23 1,095,639 12/1967 Great Britain ..174/25 C 66,588 9/1913 Switzerland ..174/1l7 FF Primary Examiner--Bemard A. Gilheany Assistant Examiner-A. T. Grimley Attorney-Webb, Burden, Robinson and Webb [57] ABSTRACT A telecommunication cable comprises at least two cable units laid up together and enclosed in a waterv proof sheath. Each cable unit comprises a multiplicity of conductors each having a dielectric of cellular plastics material, at least one layer of insulating tape,

for instance paper, surrounding the multiplicity of conductors and, filling the interstices within the cable unit, a water-impermeable medium, for instance manufacture and installation of the cable. The or each layer of insulating'tape is impregnated with the waterimpermeable medium and constitute a barrier to the ingress of water.

10 Claims, 2 Drawing Figures H-ALUMINIUM lP-CELLULAR POLYTHENE l4 EXTENSIBLE KRAFT PAPER TAPE f5-PETROLEUM JELLY I/6-PETROLEUM JELLY PATENTED on: 19 m2 POLYTHENE/ALUMINIUM LAMINATED TAPE 4 -POLYTHENE 77'ALUMINIUM f2-cELLuLAR POLYTHENE /4 EXTENSIBLE KRAFT PAPER TAPE l5-PETROLEUM JELLY IG-PETROLEUM JELLY I nvenlor DAVID LUARD BOU LT Attorney:

TELECOMMUNICATION CABLES This invention relates to telecommunication cables of the kind comprising a multiplicity of plastics insulated conductors enclosed within a water-proof sheath. If such cables, whether buried in the ground or drawn into ducts, become locally damaged to an extent to allow water to enter through the damaged sheath, the water will travel along the cable through the interstices between the insulated conductors and between the conductors and the sheath and so may have an adverse effect upon the electrical characteristics of the whole cable length, especially if there are pin holes in the plastics insulation of the conductors through which the water can permeate.

The present invention has as its object the provision of a telecommunication cable which has electrical characteristics equivalent'or approximating to those of air-filled telecommunication cables of known construction but which prevents water from travelling along the cable away from its point of entry into the cable and which is easy and clean to manipulate and/or handle both during manufacture and during subsequent installation of the cable.

In accordance with the invention the telecommunication cable comprises two or more cable units laid up together and enclosed in a water-proof sheath, each cable unit comprising a multiplicity of conductors each having a dielectric of plastics material of cellular form, one or more layers of insulating tape surrounding the multiplicity of conductors and, filling the interstices between these insulated conductors and between them and the layer or layers of insulating tape from end to end of the cable unit length, a water-impermeable medium which will not drain under the influence of gravity or such hydrostatic pressure as rnay arise in the event of damage to the cable sheath but which will permit relative sliding movement of the cellular plastics insulated conductors over one another during such bending of the cable as occurs during manufacture and installation of the cable the layer or layers of insulating tape being impregnated with the-water-impermeable medium and constituting a barrier to the ingress of water.

By making the conductor insulation of cellular plastics material, by which is meant of a material containing large numbers of non-interconnecting cells, the capacitance between the conductors of each pair or that between the conductors of each quad can be reduced to an extent substantially to compensate for the increase in inter-conductor capacitance due to the presence of water-impermeable medium in the conductor interstices throughout the cable length.

The layer or layers of insulating tapeof each cable unit serves or serve substantially to retain the water-impermeable medium within the unit during cabling and other handling of the unit during manufacture of a cable thereby substantially reducing the amount of laid up cable units before the water-proof sheath is applied. Jointing and/or terminating of the cable is also facilitated because the cable units are clean and hence easy to handle and because, when terminating a cable in a main distribution frame, after cutting back the cable sheath there is no need to provide protective papers to the exposed conductors in order to' prevent dust and other impurities contaminating the exposed conductors.

The invention also includes a method of manufacturing a telecommunication cable in accordance with the invention comprising: forming each of two or more cable units by introducing a water-impermeable medium into the insterstices between a multiplicity of conductors, each having a dielectric or plastics material of cellular form, in stages as the conductors are being assembled, and applying to the assembled conductors one or more layers of insulating tape having a porosity such that it functions as described above; laying up the cable units so formed; and enclosing the laid-up cable units in a water-proof sheath.

In assembling a cable unit the insulating tape or tapes, preferably of paper, may be lapped helically extensibility in the region of 7 to 8 percent. Such a paper is sold under the trade name Clupak.

The conductors are preferably of copper or of aluminum or an aluminum-based alloy of high conductivity, for instance a hard drawn aluminum which is at least 99.7 percent pure. The conductor insulation is preferably of cellular polythene, cellular polypropylene or cellular polyvinyl chloride.

The water-impermeable'medium used to fill the interstices within each cable unit should be one which, in addition to having the characteristics previously referred to, is compatible with the particular insulating material used to insulate the individual conductors, with the insulating material of the tape or tapes and with the material of the sheath; and which has a high co-efficient of bulk resistivity, a high dielectric strength, and preferably a low electrical permittivity.

Examples of compositions suitable for use in cables whose conductors are insulated with cellular polythene, cellular polypropylene or cellular polyvinyl chloride are:

a. Mixtures of whiting and castor oil;

b. Microcrystalline petroleum waxes;

c. Mixtures of microcrystalline petroleum waxes and oils, for instance petroleum jelly;

d. Low molecular weight, high Melt Flow Index polyethylenes of a semi-solid or grease-like nature;

e. Mixtures of petroleum jelly, microcrystalline petroleum waxes, polyisobutylene and aluminum stearate;

f. Mixtures containing cumerone indene resins;

g. A blend of two or more filling materials (a) to (f).

An example of a telecommunication cable in accordance with the invention will now be described with reference to the accompanying drawing, in which:

FIG. 1 is a cross-sectional view of the cable, and

FIG. 2- is a fragmental cross-sectional view of the cable drawn of a larger scale.

The cable comprises twelve cable units, four of whichunits 1 are of substantially sector-shaped crosssection and are laid up together to form a core and the remaining eight of which units 2 are of substantially segmental cross-section and are laid up about the core of units 1 with a lay opposite to that of the units 1.

Each cable unit 1 and 2 comprises a multiplicity of conductors l l of hard drawn aluminum, each having a dielectric 12 of cellular polythene. The insulated conductors of each unit are surround by a layer 14 of tape of extensible Kraft paper, the tape having been applied longitudinally to the assembled conductors and folded transversely around them with an overlap. The layer 14 of longitudinally applied paper tape is retained in place by an outer tape of polythene (not shown) applied helically about the cable unit. The interstices between the insulated conductors of the cable unit and between them and the layer 14 of paper tape from end to end of r the unit, are filled with petroleum jelly 15. which impregnates the layer 14 of paper tape so that it constitutes a barrier to the ingress of moisture.

The assembled cable units 1 and 2 are surrounded by a screen 3 formed from a polythene/aluminum laminated tape applied longitudinally with the polythene layer outermost and with an overlap.An extruded polythene sheath 4 is bonded to the outer polythene layer of the screen 3 and encloses the screened assembly of cable units. Petroleum jelly 16 that has, with time, exuded through the layer 14 of paper tape fills the interstices between the units 1 and 2 and betweenthe units 2 and the sheath 4.

What I claim as my invention is: 1'. A telecommunication cable comprising at least two cable units laid up together and enclosed in a water-proof sheath, each cable unit comprising a multiplicity of conductors each having a dielectric of plastics material of cellular form, at least one layer of insulating tape surrounding the multiplicity of conductors and, filling the interstices between these insulated conductors and between them and the layer of insulating tape from end to end of the cable unit length, a water-impermeable medium which will not drain under the influence of gravity or such hydrostatic pressure as may arise in the event of damage to the cable sheath but which will permit relative sliding movement of the cellular plastics insulated conductors over one another duringsuch bending of the cable as occurs during manufacture and installation of the cable, the layer of insulating tape being impregnated with the water-imf wherein the conductorsare of aluminum. 5. A telecommunication cab e as claimed n claim 1,

wherein the dielectric of the conductors is of cellular polythene.

6. A telecommunication cable as claimed in claim 1, wherein the water-impermeable'medium is petroleum jelly.

7. A telecommunication cable comprising at least two cable units laid up together and enclosed in a water-proof sheath, each cable'unit comprising a multiplicity of conductors each having a dielectric of plastics material of cellular form, at least one layer of insulating tape surrounding the'multiplicity of conductors, the layer comprising a tape applied longitudinally to and folded transversely around the multiplicity "of conductors with an overlap and, filling the interstices between these insulated conductors and between them and the layer of insulating tape from end to end of the cable unit length, a water-impermeable medium which will not drain under the influence of gravity or such hydrostatic pressure as may arise in the event of damage to the cable sheath but which will permit relative sliding movement of the cellular plastics insulated conductors over one another during such bending of the cable as occurs during manufacture and installation of the cable, the layer of insulating tape being impregnated with the water-impermeable medium and constituting a barrier to the ingress of water.

8. A telecommunication cable as claimed in claim 7, wherein the transversely folded tape is retained in place by means of a binder applied helically about the cable unit.

9. A telecommunication cable as claimed in claim 8, wherein the binder comprises a plastics tape.

10. A method of manufacturing a telecommunication cable in accordance with claim 1, comprising: forming each of at least two cable units by introducing a wat'erimpermeable medium into the interstices between a multiplicity of conductors, each having a dielectric of plastics material of cellular form, in stages as the conductors are being assembled, and applying to the assembled conductors at least one layer of insulating tape having a porosity such that it will become impregnated with the water-impermeable medium and will consitute a barrier to the ingress of water; laying up the cable units so formed; and enclosing the laid-up cable units in a water-proof sheath.

l060ll 0422 

2. A telecommunication cable as claimed in claim 1, wherein the insulating tape is of paper.
 3. A telecommunication cable as claimed in claim 2, wherein the paper is an extensible Kraft paper having an extensibility in the region of 7 to 8 percent.
 4. A telecommunication cable as claimed in claim 1, wherein the conductors are of aluminum.
 5. A telecommunication cable as claimed in claim 1, wherein the dielectric of the conductors is of cellular polythene.
 6. A telecommunication cable as claimed in claim 1, wherein the water-impermeable medium is petroleum jelly.
 7. A telecommunication cable comprising at least two cable units laid up together and enclosed in a water-proof sheath, eAch cable unit comprising a multiplicity of conductors each having a dielectric of plastics material of cellular form, at least one layer of insulating tape surrounding the multiplicity of conductors, the layer comprising a tape applied longitudinally to and folded transversely around the multiplicity of conductors with an overlap and, filling the interstices between these insulated conductors and between them and the layer of insulating tape from end to end of the cable unit length, a water-impermeable medium which will not drain under the influence of gravity or such hydrostatic pressure as may arise in the event of damage to the cable sheath but which will permit relative sliding movement of the cellular plastics insulated conductors over one another during such bending of the cable as occurs during manufacture and installation of the cable, the layer of insulating tape being impregnated with the water-impermeable medium and constituting a barrier to the ingress of water.
 8. A telecommunication cable as claimed in claim 7, wherein the transversely folded tape is retained in place by means of a binder applied helically about the cable unit.
 9. A telecommunication cable as claimed in claim 8, wherein the binder comprises a plastics tape.
 10. A method of manufacturing a telecommunication cable in accordance with claim 1, comprising: forming each of at least two cable units by introducing a water-impermeable medium into the interstices between a multiplicity of conductors, each having a dielectric of plastics material of cellular form, in stages as the conductors are being assembled, and applying to the assembled conductors at least one layer of insulating tape having a porosity such that it will become impregnated with the water-impermeable medium and will consitute a barrier to the ingress of water; laying up the cable units so formed; and enclosing the laid-up cable units in a water-proof sheath. 